This invention is related to managing the changes in voltage which occur during the changing of state of a multilevel power supply controller. In a multilevel power supply controller used to provide the required voltage for efficient amplifier operation, as illustrated in U.S. Pat. No. 5,045,990, the combination of voltage sources supplying the amplifier must be switched to a different combination or state upon changes in the output voltage of the amplifier. Upon changing states to supply more or less voltage, the change in voltage is nearly instantaneous so as to create a large slew rate. The slew rate of the supply is defined as the change in voltage over time (dV/dt).
When the slew rate of the voltage supply increases in value, it must equal or exceed the amplifier slew rate if the operating voltage is to avoid momentary depletion with the amplifier output slew rate (dVo/dt) being momentarily reduced. Further, the slew rates of the resulting output power supplies cannot greatly exceed the amplifier output slew rate since such a result can overload the internal circuitry of the amplifier. This results in switching noise (glitching) occurring in the output signal of the amplifier. Also, instantaneous switching is not permissible since the resulting RFI and switch stress to the MOSFETs are excessive. Moreover, the descending slew rate of the supply must not result in momentary outputs which are less than the final amplifier state value because this would result in momentary overload in the amplifier.
Hence, it is desirable to provide a form of slew control to correct these problems. One such solution which is ideally glitchless is to fix the slew magnitude for all incrementally changing segments each segment representing the voltage level of a voltage source associated with a bit of the binary word described in the sixteen level. This solution simply makes the slew rates of the small voltage segments the same and equal in magnitude to the amplifier slew rate and a ratio of the slew rates of all larger segments equal by ratio to the magnitude of voltages of the larger segments relative to the least segment. In other words, if a segment is twice the voltage of the least segment, its slew rates are twice the slew rates of the least segment. This results in all slew rates starting and terminating at the same time and there being only one possible resultant rate, that being the desired amplifier slew rate.
There are two problems with this method. The first is that the larger segment voltage of a sixteen level controller is eight times the voltage of the least and would have eight times the slew rate. If these slew rates are not perfectly timed and aligned the resultant output of the amplifier would be overloaded by excessive change in voltage supplied to the amplifier over time (dVcc/dt). Second, very large values of slew rate (dVcc/dt) may radiate and interfere with other systems. Thirdly, not all descending codes will be decreasing by one state resulting in the amplifier overloading with excessive -dVcc/dt.